This invention entails a new apparatus for measuring electrical properties of the heart, including but not limited to impedance. The usefulness of measuring impedance is discussed at length in co-pending U.S. non-provisional Patent Application Ser. No. 13/604,168, entitled Cardio Mapping System and Method of Cardio Mapping, filed on Sep. 5, 2012, which is assigned to, Albert Einstein Healthcare Network, one of the two assignees of the subject invention.
In particular, that application, whose disclosure is specifically incorporated herein, entails apparatus and methods for arrhythmia discrimination system and methods for determining the mechanism of cardiac arrhythmia in a patient. The cardiac arrhythmia discrimination system of that application comprises a catheter and an associated processing unit. The catheter and the processing unit are arranged to measure the electrical impedance (hereinafter “impedance”) of cardiac tissue of the patient at various selected points on the endocardial/epicardial surface of the patient's heart during a spontaneously occurring or induced arrhythmia, e.g., supraventricular tachycardia, and providing the geometric position of each of the points on the patient's heart. Each of the impedance measurements and point positions are recorded by the system. The system is arranged to determine if a point on the patient's heart exhibits low impedance (Zlow), wherein Zlow≦Zmin+0.1(Zmax−Zmin), where Zmin is the minimum impedance measured and Zmax is the maximum impedance measured. The system is also arranged to discard from its impedance measurements any points associated with tissue voltage of less than 0.5 mV indicating poor contact of the catheter to the cardiac tissue, as well as any points that are too internal to the anatomic shell (e.g., >1 mm internal to a 15 degree spherical arc of curvature with a radius of 1.5-2 cm inscribed by a local group of measured points on the heart chamber shell) or points with far-field low amplitude electrograms, and evaluates the remaining points of measured impedance to determine if there is an area of a predetermined size, e.g., approximately 3.4±2 cm2 or 2.4±1.8% of the atrial surface area, having plural Zlow points therein. The system is also used for identifying coherent, rapidly conducting pathways that may be participating in reentrant circuits and to identify damaged cardiac tissues, i.e., scar tissue, that is often the substrate for micro-reentrant circuits. In accordance with one preferred aspect of that invention, the system includes a video display coupled to the processing unit and which is arranged to produce an iso-impedance map of the cardiac tissue. The iso-impedance map is colored to represent differing impedances measured by the catheter to enable a user of the system to visually analyze the color pattern of the iso-impedance map to differentiate a focal arrhythmia caused by a group of cells focally firing, from a reentrant arrhythmia caused by a macro-reentrant circuit. The iso-impedance map can be used to facilitate appropriate therapy, e.g., ablation.
Currently catheter-based measurement of local activation time, tissue voltage, and, as recently proposed in the foregoing copending patent application, tissue impedance of the heart, are used to analyze mechanisms of cardiac arrhythmias. Current catheter technology (with large surface area electrodes) results in a considerable shunt conductance that reduces amplitude and fidelity of the recorded signals and diminishes the ability to analyze arrhythmia mechanisms.
Present mapping practice involves contact of an electrical lead to the myocardium. Various electrical resistances and conductances exist in this electrical circuit. A particularly troublesome component is the shunt conductance which exists between the electrode and the surrounding blood and which attenuates all of the recorded signals substantially. Thus, there exists a need for an improved catheter that is less sensitive to the shunt conductance and which will improve the fidelity and ease of mapping such signals. The subject invention addresses that need and other needs.
All references cited herein are fully incorporated.